title: Marker-based or model-based RSA for evaluation of hip resurfacing arthroplasty? A clinical validation and 5-year follow-up.
abstract: BACKGROUND
  The stability of implants is vital to ensure a long-term survival. RSA determines micro-motions of implants as a predictor of early implant failure. RSA can be performed as a marker- or model-based analysis. So far, CAD and RE model-based RSA have not been validated for use in hip resurfacing arthroplasty (HRA).
  
  
  METHODS
  A phantom study determined the precision of marker-based and CAD and RE model-based RSA on a HRA implant. In a clinical study, 19 patients were followed with stereoradiographs until 5 years after surgery. Analysis of double-examination migration results determined the clinical precision of marker-based and CAD model-based RSA, and at the 5-year follow-up, results of the total translation (TT) and the total rotation (TR) for marker- and CAD model-based RSA were compared.
  
  
  RESULTS
  The phantom study showed that comparison of the precision (SDdiff) in marker-based RSA analysis was more precise than model-based RSA analysis in TT (p CAD < 0.001; p RE = 0.04) and TR (p CAD = 0.01; p RE < 0.001). The clinical precision (double examination in 8 patients) comparing the precision SDdiff was better evaluating the TT using the marker-based RSA analysis (p = 0.002), but showed no difference between the marker- and CAD model-based RSA analysis regarding the TR (p = 0.91). Comparing the mean signed values regarding the TT and the TR at the 5-year follow-up in 13 patients, the TT was lower (p = 0.03) and the TR higher (p = 0.04) in the marker-based RSA compared to CAD model-based RSA.
  
  
  CONCLUSIONS
  The precision of marker-based RSA was significantly better than model-based RSA. However, problems with occluded markers lead to exclusion of many patients which was not a problem with model-based RSA. HRA were stable at the 5-year follow-up. The detection limit was 0.2 mm TT and 1° TR for marker-based and 0.5 mm TT and 1° TR for CAD model-based RSA for HRA.
authors.affiliation: Orthopaedic Research Unit, Aarhus University Hospital, Tage-Hansens Gade 2, building 10A, office # 33, 8000, Aarhus, Denmark, nina.dyrberg.lorenzen@ki.au.dk.
authors.forename: Nina Dyrberg
authors.initials: ND
authors.lastname: Lorenzen
authors.forename: Maiken
authors.initials: M
authors.lastname: Stilling
authors.forename: Stig Storgaard
authors.initials: SS
authors.lastname: Jakobsen
authors.forename: Klas
authors.initials: K
authors.lastname: Gustafson
authors.forename: Kjeld
authors.initials: K
authors.lastname: Søballe
authors.forename: Thomas
authors.initials: T
authors.lastname: Baad-Hansen
mesh_terms: D000368:Aged; D001178:Arthroplasty / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006621:Hip Joint / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D059869:Radiostereometric Analysis; D013997:Time Factors